The invention relates to a furnace for Rapid Thermal Processing of wafers, comprising a housing in which there are provided:
means for supporting the wafer, PA1 heat control means capable of reflecting heat radiation to the wafer, PA1 means for generating heat radiation situated between the wafer and the heat control means. PA1 substrate.vertline.Pd.vertline.LiEuH.sub.4.vertline.GdMgH.sub. x.vertline.SiO.sub.2
The invention also relates to a method for Rapid Thermal Processing of wafers, especially semiconductor wafers.
In the manufacture of integrated circuits from semiconductor wafers (such as silicon), Rapid Thermal Processing (RTP) is gaining ground. The main advantages of RTP are the reduced temperature load of the wafers, and the reduction of the process cycle time. In an RTP furnace wafers are heated by infrared lamps. The inner walls of the furnace are provided with highly heat (infrared) reflective coatings in order to obtain a maximum heat rate and an optimum temperature uniformity during the steady state cycle. In an ideal process a heating rate of 300.degree. C./s to 1100.degree. C., an annealing time of 5 s at 1100.degree. C., and a cooling rate of 100.degree. C./s are required. A disadvantage is that during the cooling stage the heat content of the wafer cannot be dissipated quickly. A more rapid cooling rate is prevented by the highly reflective walls of the furnace. A large part of the heat emitted by the wafer will be reflected back towards the wafer. Consequently, the throughput of the wafers is reduced. By making the walls absorb heat during the cooling stage and reflect heat during the heating stage, the cooling rate will be enhanced too and hence the process cycle time reduced.
In German patent application DE-A-4141466, a description is given of a process room for RTP which has been provided with an array of rotatable lamellae between the lower and upper walls and the heat sources. These lamellae are mechanically rotatable around their longitudinal axes and function as heat control means. Each lamella has been provided on one side with a reflective gold coating, whereas the other side has been provided with a black surface. During heating, the reflective sides of the lamellae are exposed to the wafer. For rapid cooling of the wafer, the rear sides of the lamellae, which are black, are turned towards the wafer in order to absorb the heat radiation emitted by the wafer during the cooling stage. In this way, rapid cooling of the wafer could be obtained. A disadvantage is that in the known furnace the reflectors are mechanically driven, which, in most cases, is rather complicated and increases the risk of particle formation. Moreover, the heat dissipation is limited, because the lamellae have a limited heat capacity. Also the control of an individual reflector, to increase the uniformity of the temperature profile, is cumbrous.